1. Field of the Invention
This invention relates to aqueous insulating varnishes. More particularly, the invention relates to aqueous insulating polyester resin varnishes.
2. Description of the Prior Art
Hitherto, almost all insulating varnishes and particularly wire enamels are the so-called solvent-type varnishes in which an organic solvent such as cresol, xylol or naphtha is used. These conventional varnishes have disadvantages in that the solvent and gases of decomposition are dispersed in the air in the production of insulated wires and the cost is high because the solvent should be completely incinerated by a combustion furnace. Further, these organic solvents not only cause environmental problems such as air pollution but also the working environment is deteriorated because of their bad smell, and fire is always a hazard due to the flammability of the solvents. Recently, it is particularly desired to obtain insulating varnishes which do not have these disadvantages which give rise to a poor environment.
Of wire enamels, polyester resin varnishes have particularly been employed most widely due to their properties, processability and relatively low cost involved. Hence, it has been especially desired to develop polyester resin varnishes which do not cause environmental problems. However, a polyester resin varnish which satisfies the requirement of properties and the like has not yet been provided.